For GPR fans: Probes are needed to confirm, but the first image appears to be two steel beams within a concrete beam encasement, and the second image, taken down the center line perpendicular to the first, appears to be the end of one steel beam and the beginning of another.  Of course, many perpendicular and parallel scans were performed to support this interpretation.  The rebar (hyperbolas) make it difficult to measure the width of the suspected steel beams.